DESCRIPTION

The exec family of functions replace the current process image with a new
process image. The functions described in this manual page are front-ends
for the function execve(2). (See the manual page for execve for detailed
information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which
is to be executed.
The const char *arg and subsequent ellipses in the execl(), execlp(), and
execle() functions can be thought of as arg0, arg1, ..., argn. Together
they describe a list of one or more pointers to NUL-terminated strings
that represent the argument list available to the executed program. The
first argument, by convention, should point to the file name associated
with the file being executed. The list of arguments must be terminated by
a null pointer.
The execv() and execvp() functions provide an array of pointers to NUL-
terminated strings that represent the argument list available to the new
program. The first argument, by convention, should point to the file name
associated with the file being executed. The array of pointers must be
terminated by a null pointer itself.
The execle() function also specifies the environment of the executed pro-
cess by following the null pointer that terminates the list of arguments
in the parameter list or the pointer to the argv array with an additional
parameter. This additional parameter is an array of pointers to NUL-
terminated strings and must be terminated by a null pointer itself. The
other functions take the environment for the new process image from the
external variable environ in the current process.
Some of these functions have special semantics.
The functions execlp() and execvp() will duplicate the actions of the
shell in searching for an executable file if the specified file name does
not contain a slash ('/') character. The search path is the path speci-
fied in the environment by PATH variable. If this variable isn't speci-
fied, _PATH_DEFPATH from <paths.h> is used instead, its value being:
/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin
In addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve returned
EACCES), these functions will continue searching the rest of the search
path. If no other file is found, however, they will return with the glo-
bal variable errno set to EACCES.
If the header of a file isn't recognized (the attempted execve returned
ENOEXEC), these functions will execute the shell with the path of the
file as its first argument. (If this attempt fails, no further searching
is done.)

RETURN VALUES

If any of the exec functions return, an error has occurred. The return
value is -1, and the global variable errno will be set to indicate the
error.

FILES

/bin/sh default shell program

ERRORS

execl(), execle(), execlp(), and execvp() may fail and set errno for any
of the errors specified for the library functions execve(2) and
malloc(3).
execv() may fail and set errno for any of the errors specified for the
library function execve(2).

SEE ALSO

STANDARDS

Historically, the default path for the execlp() and execvp() functions
was .:/bin:/usr/bin. This was changed to improve security and behaviour.
The behavior of execlp() and execvp() when errors occur while attempting
to execute the file is historic practice, but has not traditionally been
documented and is not specified by the POSIX standard.
Traditionally, the functions execlp() and execvp() ignored all errors ex-
cept for the ones described above and ENOMEM and E2BIG, upon which they
returned. They now return if any error other than the ones described
above occurs.
execl(), execv(), execle(), execlp() and execvp() conform to IEEE Std
1003.1-1988 ("POSIX").
MirOS BSD #10-current January 24, 1994 1